1. Field of the Invention
The present invention relates to an electroconductive rubber roller. More particularly, the present invention relates to the electroconductive rubber roller that is used preferably as a development roller provided in an image-forming mechanism of a laser printer and the like to make toner adhere to a photosensitive member. The development roller is superior in its toner-transporting performance and in charging the toner.
2. Description of the Related Art
In recent years, electrophotographic apparatuses such as a laser printer form images having a high quality at a high speed. In the laser printer, a photosensitive member directly connected to image formation and members disposed in the vicinity thereof are demanded to have high accuracy and a high speed (high response) in an initial process in an image-forming operation. Accordingly it is essential for the development roller to have high electrostatic property because the development roller used in the image-forming mechanism of the laser printer receives charged toner uniformly and supply the received toner uniformly to an electrostatic latent image formed on the photosensitive member.
The development roller having the above-described role is conventionally is of a magnet type. But with increased adoption of a system in which spherical single-component toner whose diameter can be reduced and carrier particles are not used, the development roller is increasingly made of a semi-electroconductive elastic material such as rubber instead of a magnet type as the present tendency.
The development roller is demanded to transport the toner to the photosensitive member favorably and charge the toner favorably. It is known that the toner-transporting performance of the development roller depends on the electric charge of the toner and the power of static electricity that is determined by a developing electric field. The developing electric field is determined by the kind of a developing electrode and the positional relationship between the development roller to which a bias voltage is applied and the photosensitive member on which an electrostatic latent image is formed, namely, the electric potential thereof.
In a system in which two-component toner and a carrier are used, the toner can be transported easily owing to electric and magnetic actions. The development roller used in the system employing the single-component toner is incapable of displaying a magnetic force. Thus in the system employing the single-component toner, the development roller is demanded to have a uniform surface which constitutes the end surface of the electrode. That is, the surface of the development roller is required to have a high degree of accuracy. When the bias potential is applied to the development roller, a very uniform distribution of the electric potential is required so that the electrical characteristics of the development roller such as the electric resistance is very uniform.
Because the carrier is not used in the system employing the single-component toner, the development roller is demanded to have the function of controlling the electrostatic property of the toner. When the charged quantity of the toner is insufficient, the toner cannot be transported faithfully to the electrostatic latent image on the photosensitive member owing to shortage of the power of static electricity. Consequently defective images are formed. For example, a concentration change, a ghost image, and fog are generated owing to the rotation of the development roller. Various proposals are made to solve the problems.
For example, the rubber material is disclosed in Japanese Patent Application Laid-Open No. 2002-194203 to provide the rubber layer of the development roller with a uniform electric resistance. In this proposal, the rubber material contains not an electroconductive filler but calcium carbonate, whose particles have the specified diameter, dispersed in ionic-conductive epichlorohidrin rubber to control the electric resistance of the rubber layer of the development roller by ionic conduction.
In the disclosure made in Japanese Patent Application Laid-Open No. 2001-357735, the surface of the electroconductive member is treated with a treating agent having an amine compound to control the electrostatic property of toner.
Although the rubber material disclosed in Japanese Patent Application Laid-Open No. 2002-194203 makes the electric resistance of the rubber layer uniform to some extent, the rubber material is incapable of providing toner with favorable electrostatic property nor allowing the toner to have the charged electrostatic property for a long time. Therefore the development roller made of the rubber material does not provide a preferable printed image.
According to the disclosure made in Japanese Patent Application Laid-Open No. 2001-357735, the surface of the electroconductive member of the development roller or the like cannot be treated very accurately with the treating agent. Thus the rubber material is incapable of allowing the formation of a high-quality image. Since the material of the development roller is different from that of the coating agent, there is a possibility that the coating agent peels off from the material of the development roller during production and the use thereof. It is difficult to control both the toner-transporting performance and the electrostatic property of the toner.